This invention relates to an apparatus for locking the openable parts of protective covers in textile machines, particularly machines for the spinning preparation such as carding machines, roller card units, bale openers, cleaners, fine openers and the like which have rotary components such as shafts, drums, cylinders, rollers and the like. Conventionally, such apparatus includes devices which monitor the standstill of the rotary components and actuating members which are controlled by the standstill monitors and which effect a locking or an unlocking of the movable cover parts.
In textile machines of the above type, rotary cylinders are present which represent a significant safety hazard for the operating personnel. For this reason such cylinders are, as a rule, covered by doors or other devices which prevent inadvertent touching. Since such rotary components, because of their large mass, have an inertia run of several minutes after power switch-off and which have to be routinely serviced by maintenance work, the need arises to monitor their rotation and permit an opening of the doors or other covering devices only after such rotary components are at a standstill to thus prevent access to the components when the protective covering is not in place and the component may still rotate.
In a known apparatus of the above-outlined type a tachogenerator is used as the standstill monitor which is coupled with the shaft of the main cylinder of a carding machine. The tachogenerator is connected to a circuit by a voltage measuring relay; the circuit controls the locking and unlocking of the protective cover. During operation, the tachogenerator delivers current as long as the carding cylinder rotates. Upon standstill of the carding cylinder the locking device is released so that the protective cover may be opened. It may occur, however, that a defect in some components, for example, a wire breakage, causes a false indication of "cylinder stopped" instead of "cylinder rotates". Thus, in case of such a defect, even if the cylinder is still rotating, the current from the tachogenerator is not transmitted, as a result of which the protective cover will be prematurely unlocked, thus significantly increasing the risks of accidents. Furthermore, the above-outlined conventional apparatus is relatively complex.